Abstract

The primary aim of this study was to quantify the relationship between corneal structure and
hydration in humans and pigs. X-ray scattering data were collected from human and porcine
corneas equilibrated with polyethylene glycol (PEG) to varying levels of hydration, to obtain
measurements of collagen fibril diameter, interfibrillar spacing and intermolecular spacing.
Both species showed a strong positive linear correlation between hydration and interfibrillar
spacing2
and a non-linear, bi-phasic relationship between hydration and fibril diameter,
whereby fibril diameter increased up to approximately physiological hydration, H = 3.0, with
little change thereafter. Above H = 3.0, porcine corneas exhibited a larger fibril diameter than
human corneas (p < 0.001). Intermolecular spacing also varied with hydration in a bi-phasic
manner but reached a maximum value at a lower hydration (H = 1.5) than fibril diameter.
Human corneas displayed a higher intermolecular spacing than porcine corneas at all
hydrations (p < 0.0001). Human and porcine corneas required a similar PEG concentration to
reach physiological hydration, suggesting that the total fixed charge that gives rise to the
swelling pressure is the same. The difference in their structural responses to hydration can be
explained by variations in molecular crosslinking and intra/interfibrillar water partitioning.